1. Field of the Invention
The present invention relates to a sheet processing apparatus and an image forming system, and more particularly, to a sheet processing apparatus that aligns sheet-like recording media such as paper sheets, transfer paper, printing paper, and OHP transparent sheets (in the present specification and claims, referred to as sheets) conveyed thereto, and an image forming system that includes the sheet processing apparatus and an image forming apparatus such as a copying machine, a printer, a facsimile, and a digital multi-function peripheral (MFP) having two functions of the foregoing.
2. Description of the Related Art
In an image forming apparatus such as a laser printer and a color image copying machine using electrophotography, in general, image data input from a personal computer or an image input device is exposed by laser and the like, and an electrostatic latent image is formed on an image carrier such as a photosensitive drum. After the electrostatic latent image is developed with toner by a developing unit, the toner is transferred onto a sheet and is subsequently fused on the sheet by a fixing unit of heating roller type to fix the image onto the sheet, and the sheet is then discharged. In the image forming apparatus, image forming may be performed by, other than electrophotography, using a known image forming engine such as droplet discharge (for example, inkjet) and thermal transfer.
For such an image forming apparatus, provided is a sheet processing apparatus that achieves automation of work by connecting an apparatus that performs post-processing such as alignment, stapling (stitching), punching, sort and collation, binding, and folding. Such a sheet processing apparatus that performs post-processing on sheets on which images are recorded by the image forming apparatus is referred to as a sheet post-processing apparatus as it performs the processing on the sheets after the image forming is performed. In the following description, the sheet processing apparatus is described as a sheet post-processing apparatus.
As a sheet post-processing apparatus of this type, for example, known is the technique disclosed in Japanese Patent Application Laid-open No. 2009-286509. The technique attempts to improve alignment of sheets when feeding the sheets from conveying paths of a plurality of routes into a relay conveying device that temporarily stacks therein the sheets on which images are formed and then discharges the sheets after processing. When a plurality of sheets are made to overlap and are conveyed from a sheet conveying path to an intermediate stacker serving as the relay conveying device, a part of the sheets is made to precede the other part at an initiation stage of conveyance and the sheets are then conveyed while retaining the preceding condition so as to stabilize the preceding amount at all times, thereby improving the alignment at a subsequent processing stage to achieve downsizing of the apparatus.
In the technique disclosed in Japanese Patent Application Laid-open No. 2009-286509, to improve the alignment of sheets when feeding the sheets from the conveying paths of the multiple routes to the relay conveying device, a part of the sheets is made to precede the other parts at an initial stage and the sheets are conveyed while retaining the preceding condition to improve the alignment at a subsequent processing stage. However, the subsequent processing stage is one stage, and it is not contemplated for a plurality of processing stages. In other words, a conventional apparatus that makes sheets overlap assumes a single conveying path, not supporting the conveyance to a plurality of trays. Therefore, while it may be better not to precede the others depending on a destination tray or the type of paper in some cases, the conventional apparatus is not capable of dealing with such cases.
Therefore, there is a need for a sheet processing apparatus and an image forming system capable of improving the alignment of sheets in a tray depending on the tray of a conveying destination or on the type of paper in the tray.